The invention relates to a method of manufacturing an optoelectronic semiconductor device whereby a surface of a semiconductor body, which is built up from a number of semiconductor material layers epitaxially grown on a semiconductor substrate with a top layer of GaAs adjoining the surface and a subjacent layer comprising InP, is provided with an etching mask, after which the top layer and the subjacent layer are locally etched away in a plasma which is generated in a gas mixture comprising SiCl.sub.4 and Ar.
Such an optoelectronic semiconductor device is, for example, a diode laser. In that case, for example, a layer comprising InP of (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P with a thickness of approximately 1 .mu.m is present below a top layer of GaAs with a thickness of approximately 0.3 .mu.m. Below this, furthermore, there is an approximately 0.1 .mu.m thick layer of Ga.sub.0.5 In.sub.0.5 P, also called active layer, and an approximately 1 .mu.m thick layer of (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y P. The active layer with a refractive index of approximately 3.65 lies enclosed between two layers with a lower refractive index of approximately 3.44 (when 0.5&lt;x&lt;0.8 and 0.4&lt;y&lt;0.6). Light with a wavelength of approximately 670 nm generated in the active layer is confined in the active layer in such a layer package. The top layer of GaAs is strongly doped in practice and provided with an electrode. The top layer and the subjacent InP-containing layer are locally etched away, so that a ridge is formed in these layers. The top layer is provided with an electrode. During operation, an electric current is passed through the layers via this electrode, so that light is generated in that portion of the active layer which is situated immediately below the ridge. The ridge is formed in the top layer and the subjacent in the case of a laser. A layer structure designed for this purpose may also be used as a waveguide. In that case, etching is often continued until the ridge also extends into the layer situated below the active layer. Light guided into the active layer is then confined in the active layer, just as in the case of the laser diode.
M. B. Stern and P. F. Liao in "Reactive etching of GaAs and InP using SiCl.sub.4 ", J. Vac. Sci. Technol. B 1 (4), October-December 1983, pp. 1053-1055, disclose a method whereby an etching mask of NiCr is provided on the surface of layers of GaAs and of InP, after which the layers are etched in a plasma generated in a gas mixture comprising SiCl.sub.4 and Ar. The addition of Ar to the gas mixture suppresses redeposition of material from the plasma onto the surface to be etched. The addition of Ar moreover results in etched ridges with comparatively steep edges.
It is found in practice that the known etching process is not satisfactory when a ridge as mentioned above is formed in the top layer of GaAs and in the subjacent layer comprising InP. Especially during etching of the layer comprising InP, a very rough surface is created with crests and troughs which are locally equally high as the ridge itself formed in this layer. The walls of the ridge formed in the layer are also rough. An optoelectronic semiconductor device which exhibits the said desired light confinement cannot be realized by the known method described.